Process of purifying bauxite.



No. 677,207. Patentad June 25, 19m.

' c. m. HALL.

PROCESS OF PURIFYINGBAUXITE.

I (Applicltion filed Dec. 19, 1900.)

(No Model.) I

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UNITED STATES I PATENT OFFICE.

CHARLES, M. HALL, OF NIAGARA FALLS, NEW YORK.

PROCESS OF PURlFYlNG BAUXITE.

$PEC1FICATION forming part Of Letters Patent No. 677,207, dated June 25,1901.

Application filed December 19, 1900.

To all whom it may concern:

Be it known that I, CHARLES MARTIN HALL, of Niagara Falls, in the countyof Niagara and State of New York, have invented a new and useful Processof Purifying Bauxite or other Impure Oxid of Aluminium, of which the following is a full, clear, and exact description.-

It is a matter of great importance in the manufacture of aluminium thatthe alumina to be electrolyzed should be free from impurities, for thecharacter of the ore determines largely the quality of the aluminiumwhich is produced from it. Heretofore bauxite has been purified commonlyby a chemical process which consists in converting the alumina ofbauxite into aluminate of soda, dissolving the same in water, filtering,and precipitaa ing by carbonic dioxid or by agitation, thus yielding aprecipitate of hydrate of alumina, which must be Washed, dried, andcalcined at a bright-red heat. In this process the number of reagentsemployed, particularly the soda and the carbonicdioxid, and theoperations required all add to the expense of manufacture, making thecost of the finished alumina many times that of the crude ore.

The object of my invention is'to provide a process of manufacture bywhich purified alumina can be obtained directly from the impure ore at acomparatively low cost and with many other advantages in respect ofpurity of product and simplicity of apparatus, which render my processof great practical value. Attempts heretofore made to separate theseimpurities and to obtain pure alumina by electrolytic or reductionmethods have been unsuccessful. Thus ithas been attempt en to separatethe silica and other impurities by dissolving the impure calcinedbauxite in the fused cryolite or double fluorid bath used for themanufacture of aluminium by electrolysis and electrolyzing the same atthe comparatively low temperature of such bath with the object of firstreducing the impurities, leaving the bulk of the alumina purified andu'nreduced, afterward separating the bath containing the alumina fromthe reduced impurities, and electrolyz'ing the bath containing theunreduced alumina to produce pure aluminium. This procedure, however,was not successful, because instead of all the impurities being reducedin the initial stage of Serial No. 40.36% (No specimens.)

the operation, leaving the bath pure, as was expected, it was found thata large percentage of the impurities would remain in the bath and bybeing reduced with the alumina would contaminate the product. I havediscovered, however, that bauxite and other impure oxids of aluminiumcontaining silicon as an impurity (in which I include the silicates ofaluminium) may be purified by fusing such oxid by means of an electriccurrent without any flux or with only a small proportion of flux andsubjecting it to a reducing action for a suff cient time to reduce theimpurities, leaving the bulk of the alumina unreduced,

. the said impurities (silicon and generally titanium) as they are beingreduced being caused to combine into a fused alloy with a metal, such asiron, which alloy will segregate from the fused alumina and may bereadily removed. When the bauxite or other impure oxid of aluminiumcontains a considerable percentage of iron oxid, the iron will bereduced in the process and will furnish the metal to alloy with theimpurities; but where there is only a small percentage of iron or noiron in the aluminium oxid, or where the proportion of silica andtitanic acid therein is high relatively to the iron, it is advisable toadd iron either in the form of oxid or in metallic form, or some otherheavy metal or metallic oxid which will form a fused alloy with thereduced silicon and titanium.

I will now describe the preferable form of my process, in which I purifybauxite containing suificient iron, so that when the bauxite is fusedand the impurities reduced therefrom there will result a fused alloy ofsilicon, iron, and titanium, which will segregate in the form ofglobules or large masses and can readily be removed.

I take bauxite which may be approximately of the following composition,though the process is applicable to the treatment of bauxite of variousgrades and kinds of impurities: alumina, sixty per cent; ferric oxid,eighteen per cent, silica, two to three per cent; titanic acid, three tofour per cent., and water, seventeen per cent. I preferably calcine thebauxite to remove the water, and before cal cination I may mix with itsome powdered carbon, (charcoal, coke, &c.,) which may be in theproportion of aboutfive to ten per cent.,

in order to remove the water more com pletely and reduce to some'extentthe'contained 'oxid ofiron to the metallic'form or to a lowerstate ofoxidation, and thus lessen the work required in the subsequentoperation. I then place the bauxite in a suitable electric furnace,preferably lined with carbon, and fuse it therein, preferablyfirstmixing with it powdered carbon sufficient with that remaining fromthe previous calcination to amount to eight to ten per cent. more orless, in order 'to assist in the reduction, although this is not alwaysnecessary, since the carbon of the electrodes and of'thefurnace-liningwill suffice. A more impure. bauxite will require a greater percentageof carbon. I deem it desirable to avoid 'any' large excess of carbon,which cau'ses'a waste of tbealumina and'has a prejudicial'elfect on theworking of the process.

' I may use either a direct or an alternatingv current at anelectromotive force "of, say, twenty-five to thirty volts with asuitable 'volume. furnace of about eight'inches internal diame Workingon a small scale, with a ter, I have employed about twenty eight voltsandabout fifteen hundred amperefs. I

[subjectthe mass to the fusing action of the current for some time,depending upon the size of the operation. lVhen working on the smallscale above mentioned, I ha've found one'hoursufficient to accomplishboth the fusion of the bauxite and the reduction of the impurities.Duringthis time by the action ofthe carbon, and Where a direct currentis used and the conditions for electrolysis are present by theelectrolytic action of the current, the'iron, silicon, and titanium arereduced and unite to form a fused alloy, the

bulk of which settles to the bottom. The mass is then allowed to cooland is taken from the furnace and the iron containing the otherimpurities is separated from it,'the finerparticles of the alloy whichremain shotted through the mass being picked out by a magnet orotherwise. Whenworking on alarge scale, it may be found desirable to tapolf the purified alumina and the reduced alloy in a melted condition.

When the alumina has been removed from the furnace afterit has beenpurified as above described, it is pulverized, and in this state it maybe dissolved in fused baths and electrolyzed for the production ofaluminium, for which purpose it is well adapted by reason of its freedomfrom soda, which is always present, as an impurity in the commercialalumina madebyprocessesheretofore known.

I have not been able to obtain'the results of my invention by merefusion of the material, but have found it necessary to conductthfeprocess in such way as to generate a very intense heat,or, where thetemperature is com paratively low, so that the operation isprolonged'for a considerable time.

' In the drawing I show one form of electric furnace suitable for thepractice ofmy inventio'n.

2'is the body of the bon lining 2', a tapping-hole 3, a rod 4,constituting an electrode, and conductors 5. The melted alumina isrepresented at 6, the yet unmelted charge at 7.,and the layer ofredu'cedimpurities at 8 In this furnace the hanging electrode 4;is'connected with one'of the poles of the dynamo, and the furnacelini ugis connected with the other pole and serves as the other electrode. Imay, however, use two suspended rods, each constituting an electrode andconnected withone of the poles of the dynamo. v

While the operation is proceeding the melted alumina should be wellcovered. This may be done with a layer of un'fused' bauxite,

which may in its turn be melted,or toward the end of the operation itmay becovered with a layer of carbon or previously-purified alumina. 1

f Within the scope of my invention as defined in the claims I maymodify. the steps of the process, and may use furnaces of variousforms-such as electrical arc furnaces or incandescent furnaces,eithervof the style in which the heat is generated in the materialitself or in a mass of carb'on'in proximity to the charge. I have alsoobtained excellent results by raising the electrode slightlylabove themelted material, apparently forming an arc. The current which I thenused was an alternating current of about sixty volts and about fifteenhundred to two thousands amperes. The operation was in a furnacehavfurna'ce, having a car-- ing a cavity of about sixteen inchesdiameter and twenty-four inches deep.

I believe that I am the first to purifybeaux- .ite or impure aluminiumoxid by fusing it,

reducing and separating. from it silicon and.

titanium in the'form of a fused metallic alloy, stopping the reductionwhen the impurities are substantially reduced, and then removing thealumina from'the furnace for use.

By this operation I effect a great saving in.

the cost of manufacture of alumina and' am enabled to cheapencorrespondingly the aluminium produced by electrolysis therefrom.

I claim- 1. The method of purifying bauxite or other impure oxid ofaluminium containing silica, which consists in fusing the same with anelectric current, and while fused reducing the silica therein in thepresence of a metal capable of alloying with the silicon, causing thesilicon and said metal to unite in a fused alloy, and then removing thepurified alumina from the furnace; substantially as described.

2. The method herein described of purifying bauxite or other impure oxidof aluminium containing iron and silicon, which consists in fusing thesamewith an electric current, and while fused reducing the ironand.silicon therein, causing them tounitein a fusedalloy, and then removingthe purified alumina from the furnace foruse; substantially asdescribed.

3. The method herein described of purifying bauxite or impure oxid ofaluminium containing iron and silicon, which consists in fusing thesame, reducing the iron and silicon therein, causing the silicon toalloy with the iron whereby its separation from the alumina isfacilitated, stopping the operation nearly at the time when theimpurities are reduced, and then removing the purified alumina from thefurnace for use; substantially as described.

at. The method herein described of purifying bauxite or otherimpure oxidof aluminium containing iron, titanium and silicon, which consists infusing the same with an electric current, and while fused reducing theiron, silicon and titanium therein, causing them to unite in a fusedalloy, and then removing the purified alumina from the furnace for use;substantially as described.

5. The method herein described of purifying bauxite or other impure oxidof aluminium containing iron and silicon, which consists in fusing thesame in an electric furnace in the presence of carbon, reducing the ironand silicon therein, causing the impurities to unite in the form of analloy, whereby their separation from the alumina is facilitated,and

afterward removing the purified alumina for use; substantially asdescribed. I I

6. The method herein described of puritying bauxite or other impure oxidof aluminium containing iron and silicon,which consists in fusing thesame, reducing the impurities therein and causing them to separate inthe form of a molten alloy and to settle to the bottom of the fusedmass, and then removing the purified alumina for use; substantially asdescribed. 1;

7. The method herein described of purifying bauxite or other impure oxidof aluminium, which consists in calcining the same in admixture withcarbon, fusing the calcined material in an electric furnace, reducingthe impurities and then removing the purified alumina for use;substantially as described.

8. The method herein described of purifying impure bauxite low in ironand containing silicon, which consists in adding to it a heavy metalorcompound of said metal capable of alloying with silicon, fusing thebauxite and reducing the impurities and causing them to separate in theform of an alloy with the metal so added; substantially as described.

In testimony whereof I have hereunto set my hand.

CHARLES M. HALL.

Witnesses:

W. S. FERGUSON, K. M. FLAHERTY.

